Narrow viewing angle plastic leaded chip carrier

ABSTRACT

The PLCC package enables a narrow viewing angle without requiring a second lens by providing the PLCC package with a reflector cup having multiple stages where the geometry or some other characteristic of one stage is different from the geometry or some other characteristic of another stage.

This application is a continuation of U.S. patent application Ser. No.13/025,603 filed in the United States on Feb. 11, 2011, which is herebyincorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure is generally directed toward light emittingdevices and packages for the same.

BACKGROUND

Light Emitting Diodes (LEDs) have many advantages over conventionallight sources, as incandescent, halogen and fluorescent lamps. Theseadvantages include longer operating life, lower power consumption, andsmaller size. Consequently, conventional light sources are increasinglybeing replaced with LEDs in traditional lighting applications. As anexample, LEDs are currently being used in flashlights, camera flashes,traffic signal lights, automotive taillights and display devices.

Among the various packages for LEDs, an LED package of interest is thePlastic Leaded Chip Carrier (PLCC) package for a surface mount LED.Surface mount LEDs in PLCC packages may be used, for example, inautomotive interior display devices, electronic signs and signals, andelectrical equipment.

In some LED applications, a narrow viewing angle LED is required. Asused herein, a narrow viewing angle refers to limiting the viewing angle(also referred to as the spatial radiation pattern) of less than orequal to 80 degrees (i.e., less than or equal to 40 degrees off-axis).When the LED is packaged within traditional PLCC and the LED naturallyemits light at a relatively wide viewing angle, the PLCC package must bemodified to accommodate a narrow viewing angle.

As can be seen in FIG. 1, traditional PLCC packages 100 for LEDs includecast epoxy/silicone on a plastic molded lead frame 104 which includes aplastic molded cup 108 and one or more leads which constitute a leadframe 112. Traditional plastic molded lead frames 104 are provided witha reflector cup into which the LED is mounted. The reflector cup intraditional plastic molded lead frames 104 is generally uniform innature in that the inner wall of the reflector cup has a single offsetor tilt angle relative to the surface on which the LED is mounted. If awhite LED is desired, then epoxy/silicone can be provided in thereflector cup with phosphor. In previous solutions, a narrow viewingangle was achieved for PLCC packages 100 by attaching a lens 116 to theplastic molded cup 108. The profile of the lens 116 is specificallyformed to minimize the viewing angle of the LED in the PLCC package.

There are several downsides to utilizing a lens 116 to achieve a narrowviewing angle. First, the addition of more components to the PLCCpackage increases its cost. Second, the lens 116 is usually attachedwith glue, which is also a complicated process and is not necessarilythat easy to control. Third, the viewing angle for the LED will not beaccurate if the lens 116 is tilted in any way or offset relative to theLED during the assembly process.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described in conjunction with the appendedfigures:

FIG. 1 is a perspective view of a PLCC package in accordance withembodiments of the prior art;

FIG. 2A is a perspective view of a PLCC package without an encapsulantin accordance with embodiments of the present disclosure;

FIG. 2B is a cross-sectional view of a PLCC package without anencapsulant in accordance with embodiments of the present disclosure;

FIG. 3A is a perspective view of a PLCC package with an encapsulant inaccordance with embodiments of the present disclosure;

FIG. 3B is a cross-sectional view of a PLCC package with an encapsulantin accordance with embodiments of the present disclosure; and

FIG. 4 is a flow diagram depicting a PLCC package manufacturing processin accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

The ensuing description provides embodiments only, and is not intendedto limit the scope, applicability, or configuration of the claims.Rather, the ensuing description will provide those skilled in the artwith an enabling description for implementing the described embodiments.It being understood that various changes may be made in the function andarrangement of elements without departing from the spirit and scope ofthe appended claims.

Furthermore, although the depicted PLCC package 200 is a conventionalC-bend PLCC, embodiments of the present disclosure are not so limited.In particular, embodiments of the present disclosure can be utilized inany type of known PLCC package and/or platform. Specifically, any typeof PLCC package and/or platform or similar type of package for a lightemitting device that uses a plastic molded lead frame can incorporateone or more features disclosed herein. Suitable types of PLCC packagesthat may incorporate embodiments of the present disclosure include,without limitation, a Moonstone Package which has one or more leadsprotruding to its side, an L-bend PLCC, a PLCC with one or more leadsprotruding from its bottom, and so on. One example of a PLCC packagethat may incorporate embodiments of the present disclosure is describedin further detail in U.S. Patent Publication No. 2010/0264436 to Chuanet al., the entire disclosure of which is hereby incorporated herein byreference.

With reference now to FIGS. 2A, 2B, 3A, and 3B, a PLCC package 200 willbe described in accordance with at least some embodiments of the presentdisclosure. Initially referring to FIGS. 2A and 2B, a PLCC package 200that has not yet had its reflector cup 220 filled with an encapsulant isdepicted in accordance with at least some embodiments of the presentdisclosure.

The PLCC package 200 may comprise a plastic molded lead frame 204 whichincludes a lead frame 212 having one or more leads 218 and a plasticmolded cup 208. In some embodiments, the plastic molded cup 208 may beconstructed of any polymer or combination of polymers using extrusion,machining, micro-machining, molding, injection molding, or a combinationof such manufacturing techniques.

The lead frame 212 may comprise a number of leads 218 for carryingelectrical current to and from a light source 216. The leads 218 may beexposed in the bottom of a reflector cup 220 that has been formed in theplastic molded cup 208. The leads 218 may then extend or pass throughpart of the plastic molded cup 208 to an outer surface of the plasticmolded cup 208, thereby facilitating attachment of the PLCC package 200to an electrical circuit. Although the leads 218 of the lead frame 204extending to the outer surface of the plastic molded cup 208 aredepicted a C-leads, embodiments of the present disclosure are not solimited. In particular, any other type or shape of leads may be utilizedsuch as, for example, SOJ leads, gull wing leads, reverse gull wingleads, and straight cut leads.

The reflector cup 220 may be formed in a top portion 228 of the plasticmolded cup 208 and the leads 218 may extend partially through a bottomportion 224 of the plastic molded cup 208. A top surface of the bottomportion 224 may interface with a bottom surface of the top portion 228and this interface may also correspond to the bottom surface of thereflector cup 220. The top surface of the top portion 228 may correspondto the light emitting surface of the PLCC package 200 as it has theopening of the reflector cup 220. In some embodiments, the area of thereflector cup 220 is larger at the top surface of the top portion 228 ascompared to the bottom surface of the top portion 228. This means thatthe reflector cup 220 gets larger as it extends away from the lightsource 216.

The light source 216, in some embodiments, comprises an LED or array ofLEDs. Where an LED or similar light source is used, a bonding wire 222may be used to connect a top surface of the light source 216 to one ofthe leads 218 while the bottom surface of the light source 216 isconnected to a different one of the leads 218 One surface of the lightsource 216 may correspond to an anode of the light source 216 andanother surface of the light source 216 may correspond to a cathode ofthe light source. By connecting the light source 216 to two differentleads 218 an electrical potential can be applied to the anode andcathode of the light source 216 thereby energizing the light source 216and causing it to emit light. In some embodiments, the light source 216is configured to emit light from its top surface.

Although a light source 216 is depicted as having an anode and cathodeon opposite major surfaces, embodiments of the present disclosure alsocontemplate the utilization of a light source 216 having both an anodeand cathode on the same surface. Such a light source 216 may beconstructed using known flip-chip manufacturing processes or any otherknown method for establishing both an anode and cathode on a common sideof a light source 216. In such an embodiment, multiple bonding wires maybe used to connect to the anode and cathode separately.

In some embodiments, the PLCC package 200 includes a reflector cup 220to control the direction in which the light emitted by the light source216 exits the PLCC package 200. More specifically, the light source 216may not be configured to emit a focused beam of light from its topsurface, but rather may radiate light in a spread radial pattern. Thenatural view angle of light emitted by the light source 216 may varyfrom 8 to 160 degrees (i.e., 4 to 80 degrees of off-axis view angle). Inembodiments where the light source 216 naturally emits light at aviewing angle greater than a preferred viewing angle, it may benecessary to configure the PLCC package 200 to control the angle 8 oflight which exits the PLCC package 200.

As will be discussed in further detail herein, the reflector cup 220 maybe provided with a number of optical features which allow it to controlthe angle 8 at which light exits the PLCC package 200, in particular bykeeping the light exiting the PLCC package 200 at a narrow viewingangle. As one example, the reflector cup 220 may be at least partiallyfilled with an encapsulant and/or may contain one or more features whichlimit the angle θ of light exiting the PLCC package 200 to be less than100 degrees. Such a view angle corresponds to an off-axis angle θ/2 oflight exiting the PLCC package 200. As another example, the reflectorcup 220 may be at least partially filled with an encapsulant and/or beformed to limit the angle θ of light exiting the PLCC package 200 to beless than 80 degrees. As another example, the reflector cup 220 may beat least partially filled with an encapsulant and/or be formed to limitthe angle θ of light exiting the PLCC package 200 to be less than 50degrees. More specifically, any viewing angle θ between 0 and 100degrees can be achieved by altering the optical features of thereflector cup 220.

In some embodiments, the reflector cup 220 is configured with aplurality of stages 232, 236, where each stage comprises at least onedifferent optical property than at least one of the other stages.Differing optical properties may be achieved, for example, by alteringthe geometry of one stage as compared to another. As can be seen in FIG.2B, a first stage 232 may comprise a first reflective surface 240 and asecond stage 236 may comprise a second reflective surface 244.

A transition point 242 may exist between the first and second stages232, 236. In some embodiments, the transition point 242 may correspondto a point or area where the geometry of the reflector cup 220 changesfrom the geometry of the first stage 232 to the geometry of the secondstage 236. In some embodiments, the transition point 242 may compriseits own reflective surface and may, therefore, also be referred to asanother stage of the reflector cup 220.

Although only two stages 232, 236 are depicted and described herein,embodiments of the present disclosure contemplate configuring areflector cup 220 with two, three, four, five, six, or more differentstages where each stage comprises a different geometry from that of atleast one other stage in the reflector cup 220. Specifically, theplurality of stages 232, 236 may each comprise one or more of adifferent off-axis tilt (i.e., angle at which the reflective surface240, 244 is tilted relative to a line which is orthogonal to the base ofthe reflector cup 220), a different height, a different bottom area, adifferent top area, a different shape (e.g., circular, elliptical,rectangular, etc.), or combinations thereof.

Differing optical characteristics may also be achieved by alteringfeatures or characteristics of the reflective surfaces 240, 244 from onestage to the next. Altering the feature or characteristics of thereflective surfaces 240, 244 may be done as an alternative to or inaddition to altering the geometry between stages. As one example, thefirst reflective surface 240 may be formed by or be coated with a firstmaterial that has a first reflectance whereas the second reflectivesurface 244 may be formed by or be coated with a second material thathas a second reflectance that differs from the first reflectance.Utilizing different materials on the surfaces 240, 244 can help toachieve narrow viewing angles as well as reduce light loss. Inparticular, if the second reflective surface 244 has a higherreflectance than the first reflective surface 240, then I-V degradationissues may be minimized and a better performing PLCC package 200 can beachieved. As another example, the first reflective surface 240 may besmooth whereas the second reflective surface 244 may be roughened.

Yet another way to alter optical characteristics between stages 232, 236may be to fill each stage with a different encapsulant or fill somestages with an encapsulant while not filling other stages with anencapsulant. As can be seen in FIGS. 3A and 3B, one or more of thestages may be filled with an encapsulant 260 whereas other stages maynot be filled with the encapsulant or may be filled with an encapsulantof a different type. The encapsulant 260 may be provided for a number ofpurposes. First, the encapsulant 260 may be configured to alter thecolor of light emitted by the light source 216 before it is emitted bythe PLCC package 200. Second, the encapsulant 260 may be provided tochange the index of refraction between stages. More specifically, theencapsulant 260 may have a higher index of refraction than ambient air.If the first stage 232 is filled with the encapsulant 260 and the secondstage 236 is not, light will bend at the transition point 242 betweenthe first stage 232 and second stage 236. Likewise, if the first stage232 is filled with a first type of encapsulant 260 and the second stage236 is filled with a second type of encapsulant that has a differentindex of refraction, then light will bend at the transition point 242between the first stage 232 and second stage 236. In some embodiments,at least the top stage may not be filled with an encapsulant.

Any number of materials may be suitable for use as the encapsulant 260.Examples of such materials include, without limitation, epoxy, silicone,a hybrid of silicone and epoxy, phosphor, a hybrid of phosphor andsilicone, an amorphous polyamide resin or fluorocarbon, glass, plastic,or combinations thereof. Furthermore, different materials orcombinations of materials may be used in different stages. As onenon-limiting example, if the reflector cup 220 comprises three stages,then one stage of the reflector cup may comprise one or more of epoxy,silicone, and phosphor and another stage may either have no encapsulantor may have an encapsulant of a different type.

In embodiments where the encapsulant 260 fills one stage of thereflector cup 220 but not another, the encapsulant 260 may be level(i.e., parallel to the bottom surface of the top portion 228). Byutilizing an encapsulant 260 that is level rather than dome-shaped as inthe prior art, embodiments of the present disclosure can maintain a lowprofile PLCC package 200 while still achieving a narrow viewing angle.

As discussed above, it may also be beneficial to change the reflectanceof the reflective surfaces from one stage to the next. One way toachieve this feature is to utilize an insert 248 that has a reflectivesurface 252. The reflective surface 252 of the insert 248 may have ageometry which allows the insert 248 to be received in one or morestages of the reflector cup 220. In some embodiments, the insert 248fits within some but not all of the stages of the reflector cup. In thedepicted embodiment, the insert 248 fits within the upper-most stage(i.e., the second stage 236 of the reflector cup 220). In someembodiments, the upper-most stage comprises a higher reflectance thanthe lower-most stage. This reflectance difference may be achieved solelywith the insert 248 or by coating the reflective surfaces with differentmaterials. If the reflective surfaces are coated with differentmaterials, the materials may be deposited using any number of knowndeposition techniques such as brushing, spraying, Atomic LayerDeposition (ALD), Chemical Vapor Deposition (CVD), or the like.

In embodiments where the insert 248 only fits into one stage of thereflector cup 220, the tilt angle of the reflective surface 252 may besimilar or identical to the tilt angle of the reflective surface of thestage into which the insert 248 fits. Thus, the insert 248 may act as alining for some or all of the reflector cup 220.

The insert 248 may comprise a different reflectance than that of theplastic molded cup 208 or any coatings that are applied to thereflective surfaces 240, 244. In some embodiments, the insert 248 maycomprise a thin layer of metal or a material that has been coated orplated in a metallic or reflective substance. The reflective surface 252of the insert 248, therefore, provides a higher reflectance than thefirst reflective surface 240. The difference in reflectance between thestages of the reflector cup 220 help the reflector cup 220 to decreasethe viewing angle of light emitted by the light source 216 as it exitsthe PLCC package 200. Thus, a PLCC package 200 is provided which canachieve a narrow viewing angle without requiring a dome-shaped (i.e.,convex) or external optical lens on the upper surface of the top portion228.

With reference now to FIG. 4, a method of constructing a PLCC package200 which is suitable for narrow viewing angle applications will bedescribed in accordance with at least some embodiments of the presentdisclosure. Although the steps depicted in FIG. 4 are shown in aparticular order, those of ordinary skill in the LED manufacturing artswill appreciate that certain steps may be combined and/or the order ofsteps may be altered without departing from the scope of the presentdisclosure.

Initially, a lead frame 212 having one or more leads 218 may be provided(step 404). A plastic molded cup 208 may also be provided and areflector cup 220 may be formed in the top or upper portion 228 of theplastic molded cup 208 (step 408). In some embodiments, the plasticmolded cup 208 may be formed with an injection molding process, in whichcase the plastic molded cup 208 may comprise a single piece of plastic.However, it may also be possible to construct the plastic molded cup 208with one, two, three, or more separate parts that are connected to oneanother using a bonding or fusing process or agent. As one example, thetop portion 228 may initially be a separate piece from the bottomportion 224 and the two portions may be connected to one another usingglue, epoxy, a thermosetting resin, clamps, friction fittings, or thelike. In some embodiments, the plastic molded cup 208 is a one-pieceplastic molded compound that has been formed around the lead frame 212,which means that the various stages of the reflector cup 220 arepre-molded a priori.

In some embodiments, the plastic molded cup 208 is a single piece ofplastic that has been formed by an injection molding process. Thereflector cup 220 may be formed in the top portion 228 of the plasticmolded cup 208 by using a machining, etching, and/or stamping process.The reflector cup 220, or portions thereof, may be formed into the topportion 228 while the plastic molded cup 208 is being formed (e.g.,during the molding process). An alternative approach would be to firstform the plastic molded cup 208 and then stamp or machine the topportion 228 of the plastic molded cup 208 until the reflector cup 220has been formed. Different alternatives may be more desirable fordifferent types of PLCC packages 200. In some embodiments, a whiteplastic material may be used to form some or all of the plastic moldedcup 208 to improve the brightness of the PLCC package 200. In otherembodiments, a black plastic material may be used to form some or all ofthe plastic molded cup 208 to improve the contrast of the PLCC package200.

The plastic molded cup 208 may then be attached to the lead frame 212,thereby resulting in the plastic molded lead frame 204 (step 412). Insome embodiments, it may be possible to form the plastic molded cup 208around the lead frame 212 via a molding process rather than firstforming the plastic molded cup 208 and then attaching it to the leadframe 212. Also, it may be possible to first attach the plastic moldedcup 208 to the lead frame 212 and then form the reflector cup 220 in theplastic molded cup 208.

After the plastic molded cup 208 has been attached to the lead frame212, the method continues by mounting the light source 216 into thebottom of the reflector cup 220 and electrically connecting the lightsource 216 to the leads 218 of the lead frame 212 (step 416). Thisparticular step may include connecting the bonding wire 222 between thelight source 216 and the lead frame 212.

After the light source 216 has been electrically connected to the leads218 of the lead frame 212, at least a portion of the reflector cup 220is filled with an encapsulant 260 (step 420). The encapsulant 260 may beprovided into the reflector cup 220 using known injection techniques. Insome embodiments, the encapsulant 260 only fills a first stage 232 ofthe reflector cup 220 but not a second stage 236 of the reflector cup220. In addition to helping the PLCC package 200 achieve a narrowviewing angle, the encapsulant 260 also hermetically seals the lightsource 216 in the reflector cup 220 and protects the bonding wire 222from shifting and/or breaking.

In a next optional step not shown, an insert 248 may be positionedwithin and secured to at least a portion of the inner surface of thereflector cup 220. In some embodiments, the insert 248 may be secured tothe plastic molded cup 208 with a friction fit. In some embodiments, anadhesive may be used to secure the insert 248 to the reflector cup 220.In still other embodiments, one or more clamps, lips, or similarexternal connection members can be provided to secure the insert 248 tothe plastic molded cup 208.

As can be appreciated, the PLCC package 200 may be manufacturedindividually or in a batch manufacturing process where each stepdescribed above is simultaneously performed on a plurality of PLCCpackages 200.

Specific details were given in the description to provide a thoroughunderstanding of the embodiments. However, it will be understood by oneof ordinary skill in the art that the embodiments may be practicedwithout these specific details. For example, circuits may be shown inblock diagrams in order not to obscure the embodiments in unnecessarydetail. In other instances, well-known circuits, processes, algorithms,structures, and techniques may be shown without unnecessary detail inorder to avoid obscuring the embodiments.

While illustrative embodiments of the disclosure have been described indetail herein, it is to be understood that the inventive concepts may beotherwise variously embodied and employed, and that the appended claimsare intended to be construed to include such variations, except aslimited by the prior art.

What is claimed is:
 1. A plastic molded lead frame comprising areflector cup and a light source mounted in the reflector cup, whereinthe reflector cup is configured to reflect light emitted by the lightsource and reduce a viewing angle of the light source wherein thereflector cup comprises at least a first stage with a first reflectivesurface having a first reflective surface tilt angle, a second stagewith a second reflective surface having a second reflective surface tiltangle different than the first reflective surface tilt angle and a firstencapsulant filling the first stage but not within the second stage, andwherein the plastic molded lead frame does not include a convex orexternal lens within the reflector cup, wherein the first reflectivesurface is rough and the second reflective surface is smooth.
 2. Theplastic molded lead frame of claim 1, wherein the reflector cupcomprises a bottom area where the light source is mounted and a top areawhere light emitted by the light source exits the reflector cup andwherein the size of the bottom area is less than the size of the toparea.
 3. The plastic molded lead frame of claim 1, wherein the reflectorcup is at least one of circular, elliptical, and rectangular in shape.4. The plastic molded lead frame of claim 1, wherein the reflector cupcomprises a first stage and a second stage.
 5. The plastic molded leadframe of claim 4, wherein an encapsulant fills the first stage and notthe second stage.
 6. The plastic molded lead frame of claim 4, whereinthe geometry of the first stage is different from the geometry of thesecond stage.